In general, water supply pipes used in buildings are often provided on the inner surface with coatings for the purposes of preventing corrosion and improving durability. If water supply pipes are corroded on the inner surface, red rust build-up resulting from corrosion would restrict water flow and in extreme cases, leakage could occur. Therefore, water supply pipes are coated on the inner surface upon installation or renewal.
In the prior art, various two-part epoxy coating compositions were used for the water supply pipe coating purpose. They are generally prepared by blending an epoxy resin containing at least 10% by weight of a reactive diluent with a polyamine curing agent, blending the resulting curable resin component with at least 5% by weight of a non-reactive compound such as benzyl alcohol, and further with a coloring pigment and an inorganic filler. The epoxy resin and the polyamine curing agent are mixed such that 1.1 to 0.9 equivalent of active hydrogen of the polyamine is present per equivalent of epoxy group. See Kakiuchi Hiroshi, "New Epoxy Resins", Shokodo, 1988.
The conventional coating compositions have the problems that active hydrogen-bearing compounds used as the curing agent consume a substantial amount of chlorine added to city water for sterilization purpose and that uncured resin component gives off odor. Long-term curing and thorough cleaning are often required in order to meet the water quality standard prescribed by the Municipal Water Supply Associate. Then the working period is extended and extra piping is needed to provide water supply over a long period of construction, resulting in increased construction cost and imposing inconvenience to the users.